The effect of negative dK/dt on crack growth behavior of Alloy 182, Alloy 82 and low alloy steel in a simulated BWR water environment

SCC crack growth prediction of dissimilar metal weld in nuclear reactor internals supports is critical for BWR structural integrity assessment. SCC crack may initiate at alloy 182 and grow into alloy 82 and potentially into low alloy steel. In this situation, crack grows in the weld residual stress field and crack tip stress intensity factor, K is changing with crack growth and crack growth behavior can be affected by dK/dt as predicted by the theoretical formulation. This study investigates SCC behavior under negative dK/dt conditions on Alloy 182, Alloy 82 and SQV2A pressure vessel steel, which are prepared from a mock-up dissimilar metal weldment of Alloy 182/82/low alloy steel. Theoretical analysis based on Hall's model predicts that crack growth arrest can occur when dK/dt becomes sufficiently negative, with threshold values dependent on K and material parameters. Contoured double cantilever beam specimens were tested in simulated BWR normal water chemistry under controlled K-decreasing protocols. Experimental results for Alloy 182 showed apparent crack arrest at dK/dt = −1.44×10⁻⁵ MPa√m/s and reduced growth rates at −7.22×10⁻⁶ MPa√m/s, qualitatively consistent with theoretical predictions. Alloy 82 exhibited lower SCC susceptibility with apparent crack arrest observed under K-decreasing conditions. These findings provide experimental evidence for CGR sensitivity to dK/dt, which is relevant to plant components where cracks propagate through varying residual stress fields. However, the imposed dK/dt protocol differs from natural -dK/da testing, where extensive literature demonstrates sustained crack growth to K values below those at which apparent arrest occurred here. The results require cautious interpretation for structural integrity assessment.